Patents by Inventor Tomoo Takahara
Tomoo Takahara has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).
-
Publication number: 20120237212Abstract: There is provided an optical network system in which optical signals modulated by each of at least two modulation methods are wavelength-division-multiplexed and transferred, including: an optical transmitter configured to transmit first optical signals modulated by each of at least two modulation methods; an add-drop multiplexer configured to drop second optical signals from wavelength-division-multiplexed optical signals transferred in the optical network system, and add the first optical signals to the wavelength-division-multiplexed optical signals; an optical receiver configured to demodulate the second optical signals corresponding to each of at least two modulation methods; and a controller configured to control wavelengths of the first optical signals, the second optical signals and the wavelength-division-multiplexed optical signals so as to rearrange wavelengths of the first optical signals, the second optical signals and the wavelength-division-multiplexed optical signals so that optical signals moType: ApplicationFiled: March 14, 2012Publication date: September 20, 2012Applicant: FUJITSU LIMITEDInventors: Masato Nishihara, Tomoo Takahara, Toshiki Tanaka
-
Publication number: 20120230694Abstract: A clock signal from a single reference clock is frequency converted, and the frequency-converted signal is input to an equal-interval-optical-frequency-comb generator and a modulator of an optical modulator. By varying the electric frequency of the clock signal input to the equal-interval-optical-frequency-comb generator, frequency intervals of a frequency comb to be generated can be varied, while by selectively employing a particular optical frequency from among the continuous light beams of the generated frequency comb, a frequency comb having unequal intervals can be generated. It is also possible to vary the modulation rate by varying the clock frequency of a driving signal to be input to the optical modulator. By using a clock signal of a single reference clock, the frequency intervals of the frequency comb and the variation of the modulation rate synchronize with each other.Type: ApplicationFiled: January 10, 2012Publication date: September 13, 2012Applicant: FUJITSU LIMITEDInventors: Toshiki Tanaka, Tomoo Takahara, Shoichiro Oda, Takeshi Hoshida
-
Publication number: 20120155883Abstract: An optical receiver includes an analog/digital converter, and a control circuit. The analog/digital converter has a dynamic range at a time of converting an analog electric signal generated based on an optical signal to a digital electric signal. The dynamic range is variable, and the control circuit varies the dynamic range of the analog/digital converter based on the chromatic dispersion of the optical signal.Type: ApplicationFiled: December 13, 2011Publication date: June 21, 2012Applicant: FUJITSU LIMITEDInventors: Toshiki TANAKA, Tomoo TAKAHARA
-
Publication number: 20120148235Abstract: A communication system includes a transmitter, a receiver device, and a control circuit. The transmitter transmits an optical signal. The receiver device receives the optical signal. The control circuit reduces a power consumption of the receiver device based on an accumulated chromatic dispersion of the received optical signal. The receiver device includes a receiver, an analog/digital converter, and a digital signal processor. The receiver extracts a signal indicating a complex amplitude of the optical signal. The analog/digital converter converts the signal indicating the complex amplitude into a digital signal. The digital signal processor digitally-processes the digital signal.Type: ApplicationFiled: December 9, 2011Publication date: June 14, 2012Applicant: Fujitsu LimitedInventors: Masato Nishihara, Tomoo Takahara, Toshiki Tanaka
-
Publication number: 20120082465Abstract: A phase shift unit provides a prescribed phase difference (?/2, for example) between a pair of optical signals transmitted via a pair of arms constituting a data modulation unit. A low-frequency signal f0 is superimposed on one of the optical signals. A signal of which phase is shifted by ?/2 from the low-frequency signal f0 is superimposed on the other optical signal. A pair of the optical signals is coupled, and a part of which is converted into an electrical signal by a photodiode. 2f0 component contained in the electrical signal is extracted. Bias voltage provided to the phase shift unit is controlled by feedback control so that the 2f0 component becomes the minimum.Type: ApplicationFiled: September 10, 2010Publication date: April 5, 2012Applicant: Fujitsu LimitedInventors: Yuichi Akiyama, Takeshi Hoshida, Akira Miura, Yutaka Kai, Hiroki Ooi, Jens Rasmussen, Kentaro Nakamura, Naoki Kuwata, Yoshinori Nishizawa, Tomoo Takahara, Masahiro Yuki
-
Patent number: 8145071Abstract: An optical receiving apparatus branches an optical signal, photo-electric-converts the branched signals, and compensates dispersion in each of the converted electrical signals. Electrical-dispersion compensators respectively compensate the dispersion in the electrical signals using a transversal filter having plural taps. A dispersion control unit controls the dispersion compensation amount for each of the electrical signals by adjusting tap coefficients of the transversal filter. A delay control unit controls the difference in the delay time of the electrical signals by adjusting the tap coefficients adjusted by the dispersion control unit. An identifying circuit identifies data in the optical signal based on each of the electrical signals that have been subjected to dispersion compensation by each of the electrical-dispersion compensators.Type: GrantFiled: August 26, 2008Date of Patent: March 27, 2012Assignee: Fujitsu LimitedInventors: Toshiki Tanaka, Yuichi Akiyama, Tomoo Takahara
-
Patent number: 8073339Abstract: An optical modulation device including waveform shapers that waveform-shape input data signals in synchronism with a rising or falling timing based on comparison with a reference level of an input clock signal, a multi-level phase modulator that generates a multi-level-phase-modulated optical signal based on the data signals waveform-shaped by the plurality of waveform shapers, and outputs the generated optical signal, and a level ratio controller that varies a relative level ratio of the reference level to an amplitude level of the clock signal input to the waveform shapers, based on the optical signal output from the multi-level phase modulator.Type: GrantFiled: July 29, 2008Date of Patent: December 6, 2011Assignee: Fujitsu LimitedInventors: Masato Nishihara, Tomoo Takahara, Toshiki Tanaka
-
Publication number: 20110293276Abstract: An optical transmitter includes: a first modulator that modulates a first optical signal with a first data signal; a second modulator that modulates a second optical signal with a second data signal; a multiplexer that multiplexes the first optical signal and the modulated second optical signal to output a multiplexed signal; a phase difference data generator that generates a phase difference signal corresponding to a phase difference between the modulated first optical signal and the modulated second optical signal from the multiplexed signal; and a controller that controls the phase difference between the modulated first optical signal and the modulated second optical signal based on the phase difference signal.Type: ApplicationFiled: May 20, 2011Publication date: December 1, 2011Applicant: FUJITSU LIMITEDInventor: Tomoo TAKAHARA
-
Publication number: 20110229148Abstract: An optical modulation apparatus includes a first modulator, a second modulator, a multiplexer, a detector and an adjustor. The first modulator modulates light emitted by a light source using a first input signal and outputs a first modulated signal. The second modulator modulates the light using a second input signal and outputs a second modulated signal. The multiplexer multiplexes the first and second modulated signals and outputs a multiplexed signal. The detector is configured to detect a dip where power in a waveform of the multiplexed signal is equal to or smaller than a predetermined value. The adjustor is configured to adjust a delay of the first and second input signals based on power at the dip.Type: ApplicationFiled: March 15, 2011Publication date: September 22, 2011Inventors: Masato NISHIHARA, Tomoo Takahara, Takeshi Hoshida
-
Publication number: 20110229150Abstract: An optical modulation apparatus includes a first modulator, a second modulator, a multiplexer, a calculator and an adjustor. The first modulator configured to modulate light emitted by a light source using a first input signal and output a first modulated signal. The second modulator configured to modulate the light using a second input signal and output a second modulated signal. The multiplexer configured to multiplex the first and second modulated signals and output a multiplexed signal. The calculator configured to calculate a power difference between a higher-side frequency component having a frequency higher than a center frequency of the multiplexed signal and a lower-side frequency component having a frequency lower than the center frequency. The adjustor configured to adjust delays of the first and second input signals based on the power.Type: ApplicationFiled: March 15, 2011Publication date: September 22, 2011Applicant: FUJITSU LIMITEDInventors: Masato NISHIHARA, Tomoo TAKAHARA, Takeshi HOSHIDA
-
Patent number: 8005372Abstract: The present invention is a differential M phase shift keying optical receiving circuit to improve an identification property of a signal from an optical front-end unit having a plurality of lines. For this, the differential M phase shift keying optical receiving circuit includes: a light-electricity converter for outputting a plurality of electronic signals in which phase-modulated element is intensity modulated from a received optical signal; a data reproduction unit for reproducing a plurality of data signals synchronized with a common clock signal from the plurality of electronic signals output from the light-electricity converter; a clock signal generation unit for generating the common clock signal to be used for reproducing the plurality of data signals in the data reproduction unit with the use of one of the plurality of electronic signals output from the light-electricity converter; and a selection unit for selecting an electronic signal to be used for generating the common clock signal.Type: GrantFiled: April 24, 2007Date of Patent: August 23, 2011Assignee: Fujitsu LimitedInventor: Tomoo Takahara
-
Publication number: 20110150506Abstract: An optical receiver includes an optical front-end, a digital converter, a frequency-characteristic-difference reducing unit and an identifying unit. The optical front-end splits an input signal light into signal light components on a basis of local light and converts the split signal light components into electrical signals. The digital converter converts the electrical signals, converted by the optical front end, into digital signals. The frequency-characteristic-difference reducing unit reduces a frequency-characteristic difference between the digital signals converted by the digital converter. The identifying unit identifies each of the digital signals whose frequency-characteristic difference is reduced by the frequency-characteristic-difference reducing unit.Type: ApplicationFiled: December 2, 2010Publication date: June 23, 2011Applicant: FUJITSU LIMITEDInventors: Takahito TANIMURA, Tomoo Takahara, Takeshi Hoshida
-
Patent number: 7936993Abstract: In order to compensate for chromatic dispersion ad dispersion slope over an entire wavelength band of the optical signal, the wavelength band is split into a plurality of bands, and chromatic dispersion compensation is made to make chromatic dispersion in a central wavelength of each of the bands zero.Type: GrantFiled: December 30, 2009Date of Patent: May 3, 2011Assignee: Fujitsu LimitedInventors: Hiroki Ooi, Takashi Iwabuchi, Takafumi Terahara, Junichi Kumasako, George Ishikawa, Tomoo Takahara
-
Patent number: 7903983Abstract: An optical receiver converting an optical signal modulated by differential phase shift keying to electrical first and second data signals; generating a clock signal from the first data signal; demultiplexing the first data signal into two signals; latching the two signals using the clock signal; delaying the clock signal by a certain amount; latching the two signals using the delayed clock signal; demultiplexing the second data signal into two additional signals; generating an inverted clock signal by inverting the clock signal; latching the two additional signals using the inverted clock signal or the clock signal; and further latching the two additional signals using the delayed clock signal.Type: GrantFiled: March 27, 2008Date of Patent: March 8, 2011Assignee: Fujitsu LimitedInventor: Tomoo Takahara
-
Patent number: 7853152Abstract: A signal regeneration device which makes an extracted clock signal highly accurate while maintaining superior receiving sensitivity. To this end, a device of the present invention is configured to have a branch section for branching an input electrical signal which has been demodulated from a differential phase-shift modulated state; a first filter for equalizing a waveform of one of the demodulated electrical signals branched by the branch section; a clock recovery section for recovering a clock signal from the demodulated electrical signal whose waveform has been equalized by the first filter; and a data regeneration section for regenerating a data signal from a remaining one of the demodulated electrical signals branched by the branch section and from a clock signal recovered by the clock recovery section.Type: GrantFiled: March 24, 2006Date of Patent: December 14, 2010Assignee: Fujitsu LimitedInventors: Masato Nishihara, Tomoo Takahara, George Ishikawa
-
Patent number: 7817923Abstract: A phase shift unit provides a prescribed phase difference (?/2, for example) between a pair of optical signals transmitted via a pair of arms constituting a data modulation unit. A low-frequency signal f0 is superimposed on one of the optical signals. A signal of which phase is shifted by ?/2 from the low-frequency signal f0 is superimposed on the other optical signal. A pair of the optical signals is coupled, and a part of which is converted into an electrical signal by a photodiode. 2f0 component contained in the electrical signal is extracted. Bias voltage provided to the phase shift unit is controlled by feedback control so that the 2f0 component becomes the minimum.Type: GrantFiled: December 30, 2005Date of Patent: October 19, 2010Assignee: Fujitsu LimitedInventors: Yuichi Akiyama, Takeshi Hoshida, Yutaka Kai, Hiroki Ooi, Kentaro Nakamura, Naoki Kuwata, Yoshinori Nishizawa, Tomoo Takahara, Masahiro Yuki
-
Publication number: 20100260504Abstract: An optical transmission system includes an optical transmitter that includes first and second light sources, first and second phase modulators respectively modulating light from the first and the second light sources, and a polarized beam combiner combining the light output from the first and the second phase modulators to output an optical signal; and an optical receiver that includes a local oscillator, a polarization beam splitter splitting, according to polarization, the optical signal transmitted from the optical transmitter, and first and second digital coherent receivers corresponding to the first and the second phase modulators, and including a frontend that mixes light from the local oscillator and the polarization-split optical signal to output an electrical signal of real and imaginary parts, an analog-digital converting unit converting the electrical signal to a digital signal, and a digital signal processing unit estimating phase of the digital signal and extracting a signal.Type: ApplicationFiled: April 6, 2010Publication date: October 14, 2010Applicant: FUJITSU LIMITEDInventor: Tomoo TAKAHARA
-
Publication number: 20100178065Abstract: A delay device that provides a delay amount to at least one of the in-phase signal and the quadrature signal, and a delay control section that controls the delay amount provided by the delay device based on a quality of the signals when the in-phase signal and the quadrature signal, to the at least one of which the delay amount is provided, at the delay device are converted into digital signals by the analog-digital converter, and the digital signal processing is carried out at the processor are provided. Thereby, the signal quality of recovered data at a receiving end of a multi-level phase modulation communication system is improved.Type: ApplicationFiled: November 17, 2009Publication date: July 15, 2010Applicant: FUJITSU LIMITEDInventors: Masato Nishihara, Tomoo Takahara, Hisao Nakahima
-
Patent number: 7751706Abstract: In order to compensate for chromatic dispersion ad dispersion slope over an entire wavelength band of the optical signal, the wavelength band is split into a plurality of bands, and chromatic dispersion compensation is made to make chromatic dispersion in a central wavelength of each of the bands zero.Type: GrantFiled: November 10, 2008Date of Patent: July 6, 2010Assignee: Fujitsu LimitedInventors: Hiroki Ooi, Takashi Iwabuchi, Takafumi Terahara, Junichi Kumasako, George Ishikawa, Tomoo Takahara
-
Patent number: 7734196Abstract: A DQPSK receiver extracts first and second phase modulation components from an input optical signal, and respectively converts the extracted components into the first and second data signals. The DQPSK receiver extracts a clock signal from one of the data signals, and produces an inverted clock signal by inverting the extracted clock signal. Then, the DQPSK receiver latches the first data signal by using the extracted clock signal or the inverted clock signal, and latches the second data signal by using the extracted clock signal.Type: GrantFiled: December 21, 2005Date of Patent: June 8, 2010Assignee: Fujitsu LimitedInventor: Tomoo Takahara